<h2>题目编号 : 239</h2>
<div style="color:#666;font-size:80%;">03 April 2009</div><br />
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<p>A set of disks numbered 1 through 100 are placed in a line in random order.</p>

<p>What is the probability that we have a partial derangement such that exactly 22 prime number discs are found away from their natural positions?<br />
(Any number of non-prime disks may also be found in or out of their natural positions.)</p>

<p>Give your answer rounded to 12 places behind the decimal point in the form 0.abcdefghijkl.</p>

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